1. Field of the Invention
The melt-reaction synthesis of dibasic plumbousfatty acid salts and their use as stabilizers in the production of rigid halogen-containing polymers.
2. Statement of the Related Art
Stabilizers based on lead compounds are widely used in the production of moldings of halogen-containing polymers, particularly rigid polyvinyl chloride. Stabilizer systems of this type are not only highly effective, they are also inexpensive. In addition, they provide the plastic end products with effective light stabilization. For many years, formulations containing stabilizers based on lead compounds have normally contained primary stabilizers, (also known as pigment stabilizers) because of their covering power. These stabilizers are generally basic lead sulfates.
Other suitable stabilizers are organic lead salts, particularly lead fatty acid soaps. Of particular importance are the commercial lead stearates which are used either as dibasic lead stearate, 2 PbO.Pb(fatty acid residue).sub.2 -51% by weight lead stearate, or as neutral lead stearate Pb(fatty acid residue).sub.2 -28% by weight lead stearate. In many cases, combinations of these two are also used.
The stabilizer system is generally completed by calcium soaps, particularly commercial calcium stearate. These metal soaps may also be counted as part of the lubricant system which normally contains paraffins, optionally free fatty acids, other hydrocarbon waxes such as polyethylene derivatives, and, in some cases, fatty acid esters.
In recent years, the economic need to find less expensive formulations has resulted in the growing elimination of pigment stabilizers of the basic lead sulfate type. In addition, developments in the field of processing machines for plastics have meant that molding compositions based on halogen-containing polymers containing far less stabilizer can now be extruded without difficulty. Accordingly, the basic lead soaps 2PbO.Pb(fatty acid residue).sub.2 primarily stearates, are increasingly becoming the focus of interest as primary stabilizers. Neutral lead soaps (stearates) optionally together with calcium soaps (stearates) are being used as rheologically active constituents of the formulation and as co-stabilizers. By contrast, there has been little change in the other components of the stabilizers/lubricant systems still used for halogen-containing polymers.
Mixtures of the type in question here offer the incentive to produce the entire stabilization and rheology system in the form of a melt compound. Proposals to that effect can be found, for example, in U.S. Pat. No. 3,461,081 and U.K. Pat. No. 1,136,935, as well as their corresponding German Pat. Nos. 1,544,697 and 1,569,190. These publications describe non-dusting stabilizer/lubricant combinations for vinyl chloride polymers which comprise a mixture--combined in the melt--of lubricants, metal soaps of a long-chain aliphatic carboxylic acid and basic lead salts of inorganic or organic acids. However, experience has shown that it is difficult, if not impossible, to produce dibasic lead soaps (stearates) and, in particular, defined quantities of dibasic lead soaps in addition to neutral lead soaps (stearates), by the melt process. Accordingly, it is proposed in the above publications to introduce separately prepared dibasic lead soaps into the melt of lubricants and/or neutral lead soaps.